System and method for returning to 5g after fallback

ABSTRACT

Systems and methods described herein bring a 5G standalone-capable end device back into 5G service to leverage the 5G network&#39;s data capacity as soon as a VoLTE call is over. A network device receives a fallback connection, for a 5G New Radio (NR) standalone-capable end device, from a second network to the first network to support a voice call on the end device, wherein the fallback connection supports a voice-over-LTE call. The network device detects an end of the VoLTE call and initiates, in response to the detecting, a handover of the end device back to the second network, wherein the initiating occurs while the end device is in a radio resource control (RRC) connected mode.

BACKGROUND

Long Term Evolution (LTE) is a mobile telecommunications standard forwireless communications involving mobile user equipment, such as mobiledevices and data terminals. LTE networks include existing FourthGeneration (4G) and 4.5 Generation (4.5G) wireless networks. NextGeneration mobile networks, such as Fifth Generation (5G) mobilenetworks, are being implemented as the next evolution of mobile wirelessnetworks. 5G mobile networks are designed to increase data transferrates, increase spectral efficiency, improve coverage, increasecapacity, and reduce latency. 5G networks may use different frequencies,different radio access technologies, and different core networkfunctions than current or legacy wireless networks (e.g., 4G networks).

While 5G networks are being deployed and evolving, 5G-capable enddevices need to be supported in legacy networks, such as LTE networks.For example, the end devices may switch between different frequencybands, core networks, and radio access networks (RANs) that supporteither 4G or 5G standards. In a mobility context, mobile networkoperators need to support continuity of voice and data connectionsduring network changes to provide a good user experience for customerswhile maximizing the benefits of 5G connections.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary network environment in which systems andmethods described herein may be implemented;

FIG. 2 is a diagram illustrating exemplary communications for an enddevice within a dual coverage area in a portion of the networkenvironment of FIG. 1;

FIG. 3 illustrates functional components and connections of networks ofFIG. 1

FIG. 4 is a diagram of exemplary components that may be included in oneor more of the devices shown in FIGS. 1-3;

FIGS. 5-8 are signal flow diagrams illustrating exemplary communicationsfor triggering a return to a 5G connection after concluding a call withvoice-over-LTE (VoLTE) fallback, according to implementations describedherein; and

FIG. 9 is a flow diagram illustrating an exemplary process for bringinga 5G standalone-capable end device back into 5G service as soon as aVoLTE call is over, according to an implementation described herein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following detailed description refers to the accompanying drawings.The same reference numbers in different drawings may identify the sameor similar elements. Also, the following detailed description does notlimit the invention.

As Fifth Generation (5G) networks are being rolled out, user equipment(referred to a “UE” or an “end device”) is being configured to connectto both 5G radio access networks (also referred to as New Radio (NR)radio access networks (RANs)) and 4G RANs, such as an Evolved UMTSTerrestrial Radio Access Network (E-UTRAN) of a Long Term Evolution(LTE) network. 5G end devices may need to be supported in 4G networksbecause of coverage reasons (e.g., limited coverage areas of 5G RANs)and/or feature support (e.g., features, such as voice-over-LTE, thatrely on 4G in initial 5G deployments when voice-over-NR (VoNR) is notready).

5G-capable end devices that do not need to rely on 4G wireless stationsto establish 5G connectivity (also referred to as “NR standalone-capableend devices”) may switch between different frequency bands, corenetworks, and RANs that support either 4G or 5G standards. In a mobilitycontext, a mobile network needs to support continuity of voice and dataconnections, to provide a good user experience for customers whilemaximizing the benefits of 5G connections. However, switching betweenthe different frequency bands, core networks, and/or RANs can causeservice interruptions when an end device changes network connectionsmid-session. In some use cases, these service interruptions may notaffect the user experience. However, continuity of voice calls presentsa particular challenge in a 4G/5G mobility context, since voice servicestypically have the most stringent requirements in terms of latency anduser experience.

Thus, until voice-over-new-radio (VoNR) is supported fully (e.g., withequivalent coverage and capacity currently achieved by 4G networks forvoice-over-LTE (VoLTE)), default fallback to 4G networks is necessaryfor voice calls by 5G-capable end devices. For example, in NR coveragearea that does not support Voice (VoNR), when a voice call starts, theend device is redirected or performs an inter-RAT handover from NR toLTE when a dedicated bearer required for the voice call is set up. Fromthen on, VoLTE will be used and the end device is served by the LTEnetwork. However, after completion of a VoLTE call it is preferable tobring the end device back into the 5G service (e.g., to leverage the 5Gnetwork's data capacity) as soon as possible.

Currently, after a VoLTE call is over, there is no clearly-definedmechanism to make the end device return to the 5G network when datatraffic continues after the VoLTE call (e.g., the end device is still inradio resource control (RRC) connected mode due to data activities). Theend device is not prompted to perform higher priority network selectionuntil the end device transitions to an RRC idle mode. In order toleverage 5G networks and provide the best user experience on datathroughput and other potential services, service providers need amechanism to trigger end devices to more quickly return to 5G networksafter a VoLTE fallback.

Systems and methods described herein bring a 5G standalone-capable enddevice back into 5G service to leverage the 5G network's data capacityas soon as a VoLTE call is over. According to an implementation, anetwork device, such as a base station for a 4G network, receives afallback connection, for a 5G New Radio (NR) standalone-capable enddevice, from a second network (e.g., a 5G network) to a first network(e.g., a 4G network) to support a voice call on the end device, whereinthe fallback connection supports a voice-over-LTE call. The networkdevice detects an end of the VoLTE call and initiates, in response tothe detecting, a handover of the end device back to the second network,wherein the initiating occurs while the end device is in a radioresource control (RRC) connected mode.

FIG. 1 is a diagram of an exemplary network environment 100 in which thesystems and methods described herein may be implemented. Referring toFIG. 1, environment 100 includes user equipment (UE) 110, a RAN 120 witha wireless station 125, a RAN 140 with a wireless station 135, a corenetwork 140 with network devices 145, an IP Multimedia Subsystem (IMS)network 150, and data network (DN)/packet data network (PDN) 160. Inother embodiments, environment 100 may include additional networks,fewer networks, and/or different types of networks than thoseillustrated and described herein.

Network environment 100 includes links between the networks and betweenthe devices. For example, environment 100 may include wired, optical,and/or wireless links among the devices and the networks illustrated. Acommunication connection via a link may be direct or indirect. Forexample, an indirect communication connection may involve anintermediary device and/or an intermediary network not illustrated inFIG. 1. Additionally, the number and the arrangement of linksillustrated in environment 100 are exemplary.

In the configuration illustrated in FIG. 1, UE 110 may use wirelesschannels 170-1 and 170-2 (referred to collectively as wireless channels170) to access wireless stations 125 and 135, respectively. Wirelesschannels 170 may correspond, for example, to a physical layer inaccordance with different radio access technology (RAT) types. Forexample, wireless channel 170-1 may correspond to the physical layerassociated with 4G or 4.5G RAN standards (e.g., 3GPP standards for 4Gand 4.5G air interfaces, collectively referred to herein as “4G”), whilewireless channel 170-2 may correspond to the physical layer associatedwith 5G New Radio standards (e.g., 3GPP standards for 5G airinterfaces).

UE 110 (also referred to herein as UE device 110 or user device 110),may include any type of mobile device having multiple coverage modecapabilities (e.g., E-UTRA-NR Dual Connectivity (EN-DC) capabilities)and is able to communicate with different wireless stations (e.g.,wireless stations 125 and 135) using different wireless channels (e.g.,channels 170) corresponding to different RANs (e.g., RANs 120 and 130).UE 110 may be a mobile device that may include, for example, a cellularradiotelephone, a smart phone, a tablet, any type of internet protocol(IP) communications device, a Voice over Internet Protocol (VoIP)device, a personal computer (PC), a laptop computer, a wearable computer(e.g., a wrist watch, eye glasses, etc.), a gaming device, a mediaplaying device, etc. In other implementation, UE 110 may be implementedas a machine-type communications (MTC) device, an Internet of Things(IoT) device, a machine-to-machine (M2M) device, etc.

According to implementations described herein, UE 110 may be provisioned(e.g., via a subscriber identity module (SIM) card or another secureelement) to recognize particular network identifiers (e.g., associatedwith RANs 120 and 130) and to support particular radio frequency (RF)spectrum ranges.

RAN 120 and RAN 130 may have different RAT types. RAN 120 may include aradio access network for a 4G or advanced 4G network. For example, inone implementation, RAN 120 may include an E-UTRAN for an LTE network.RAN 130 may include a 5G NR RAN or both a 5G NR RAN and an E-UTRAN foran LTE network. For example, RAN 130 may be configured to supportcommunications via both LTE and 5G networks.

Wireless stations 125 and 135 may each include a network device that hascomputational and wireless communication capabilities. Wireless station125 may include a transceiver system that connects UE device 110 toother components of RAN 120 and core network 140 using wireless/wiredinterfaces. In the configuration of FIG. 1, wireless station 125 may beimplemented as a base station (BS), an evolved Node B (eNB), an evolvedLTE (eLTE) eNB, or another type of wireless node (e.g., a picocell node,a femtocell node, a microcell node, etc.) that provides wireless accessto one of RANs 120. Wireless station 135 may include a transceiversystem that connects UE device 110 to other components of RAN 130 andcore network 140 using wireless/wired interfaces. For example, wirelessstation 135 may include a next generation NodeB (gNB) or a combinationeNB and gNB.

Core network 140 may include one or multiple networks of one or multipletypes. For example, core network 140 may be implemented to include aterrestrial network and/or a satellite network. According to anexemplary implementation, core network 140 includes a network pertainingto multiple RANs 130. For example, core network 140 may include the corepart of an LTE network, an LTE-Advanced network, a 5G network, a legacynetwork, etc.

Depending on the implementation, core network 140 may include variousnetwork elements that may be implemented in network devices 145. Suchnetwork elements may include a mobility management entity (MME), a userplane function (UPF), a session management function (SMF), a core accessand mobility management function (AMF), a unified data management (UDM),a PDN gateway (PGW), a serving gateway (SGW), a policy control function(PCF), a home subscriber server (HSS), as well other network elementspertaining to various network-related functions, such as billing,security, authentication and authorization, network polices, subscriberprofiles, network slicing, and/or other network elements that facilitatethe operation of core network 140.

DN/PDN 160 may include one or more IP networks. The IP layer may beimplemented over a local area network (LAN), a wide area network (WAN),a metropolitan area network (MAN), a telephone network, etc., capable ofcommunicating with UE 110. In one implementation, DN/PDN 160 includes anetwork that provides data services (e.g., via packets or any otherInternet protocol (IP) datagrams) to user device 110. Some or all of aparticular DN/PDN 160 may be managed by a communication servicesprovider that also manages RAN 120, RAN 130, core network 140, and/orparticular UE devices 110. In some implementations, DN/PDN 160 mayinclude IMS network 150. IMS network 150 may include a network fordelivering IP multimedia services and may provide media flows betweentwo different UEs 110, and/or between a particular UE 110 and externalIP networks or external circuit-switched networks (not shown in FIG. 1).

The number and arrangement of devices in network environment 100 areexemplary. According to other embodiments, network environment 100 mayinclude additional devices (e.g., thousands of UE 110 s, hundreds ofwireless stations 125/135, dozens of RANs 120/130, etc.) and/ordifferently arranged devices, than those illustrated in FIG. 1.

As described above, in an exemplary implementation, UE 110 is an EN-DCdevice capable of communicating via a 4G network (e.g., an LTE network)or 4.5G network, as well as via a 5G network. In conventional systemsbased on current standards, when UE 110 may connect to a cell based onthe signal strengths of the particular wireless stations, withpreference given to wireless stations that provide 5G service.

FIG. 2 is a diagram illustrating exemplary connections for UE 110 in aportion 200 of network environment 100. FIG. 2 generally showsconnections between UE 110 and DN/PDN 160, which may be an intermediatepoint or endpoint for a voice/data session with UE 110. Particularly,FIG. 2 illustrates connections when UE 110 is within a 5G cell orcoverage area 220 (e.g., serviced by gNB 135) that is also within alarger 4G cell or coverage area 210 (e.g., serviced by eNB 125).

According to implementations described herein, when UE 110 is in the RRCidle mode and located within the coverage area of a 5G cell, UE 110 maycamp on the 5G cell (e.g., 5G cell 220), as indicated by reference 230.For voice sessions (e.g., voice session 250), UE 110 may use eNB 125 for4G cell 210 to ensure uninterrupted VoLTE mobility. For data sessions(e.g., data session 240), gNB 125 may be used with 5G cell 220 toprovide the highest connection speeds.

As described further herein, when UE 110 uses VoLTE (voice session 250)for a voice call via eNB 125, data (e.g., data session 260) also isrouted through eNB 125. If a data session continues past the end of aVoLTE call, unless prompted otherwise, the network will not handover UE110 to gNB 135 until an RCC idle state occurs. According toimplementations described herein, eNB 125 may detect the end of theVoLTE call (e.g., voice session 250) and/or a continuation of datasession 260 after the VoLTE call, and initiate a handover of UE 110 togNB 135, eliminating the handover delay after the VoLTE fallback.

FIG. 3 illustrates functional components in a portion 300 of networkenvironment 100 according to an exemplary implementation. In thisimplementation, core network 140 includes an interworking 5G and LTEcore network and may share common network elements (e.g., correspondingto one or more network devices 145). For example, core network includesa combined User Plane Function (UPF) and PDN Gateway-User Plane function(PGW-U) 320. UPF and PGW-U 320 may occupy the same physical device or asoftware module. UE 110 may access core network 140 via E-UTRAN 120/eNB125 and NR-RAN 130/gNB 135.

As shown, core network 140 includes Access and Mobility Function (AMF)306, Mobility Management Entity (MME) 316, Serving Gateway (SGW) 318,UPF+PGW-U 320, a combined session management function and PDNgateway-control plane function (SMF+PGW-C) 322, a combined policycharging function and Policy and Charging Rules Function (PCF+PCRF) 324,and a combined unified data management function and home subscriberserver (UDM+HSS) 326. Although core network 140 may have additionalnetwork nodes and/or functions that interact with one another viadifferent interfaces, they are not illustrated in FIG. 3 for simplicity.

gNB 135 may provide wireless devices, such as UE device 110, access tocore network 140. As discussed above, gNB 135 is part of an RAN 130,which may include additional wireless stations.

AMF 306 may perform registration management, connection management,reachability management, mobility management, lawful intercepts, accessauthentication and authorization, positioning services management,management of non-3GPP access networks, and/or other types of managementprocesses. gNB 135 may interact with AMF 306 via an N2 interface. UE 110may interact with AMF 306 via an N1 interface.

eNB 125 may provide access to network 312, to wireless devices, such asUE device 110. As discussed above, eNB 125 is part of RAN 120, which mayinclude additional wireless stations.

MME 316 may provide control plane processing for an evolved packet core(EPC) in network 312. For example, MME 316 may implement tracking andpaging procedures for UE device 110, may activate and deactivate bearersfor UE device 110, may authenticate a user of UE device 110 and mayinterface to non-LTE radio access networks. A bearer may represent alogical channel with particular QoS requirements. MME 316 may alsoselect a particular SGW for a particular UE device 110. MME 316 maycommunicate with eNB 125 through an S1-MME interface.

SGW 318 may provide an access point to UE device 110, handle forwardingof data packets for UE device 110, perform transport level markings(e.g., QoS Class Identifier (QCI)), and act as a local anchor pointduring handover procedures between wireless stations. In addition, SGW318 may forward messages between MME 316 and UPF+PGW-U 320. For example,when SGW 318 receives a message from MME 316 indicating that UE device110 is unavailable to accommodate a request to change the bearer, SGW318 may forward the message to UPF+PGW-U 320. SGW 318 may interact witheNB 125, MME 316, and PGW 320 over an S1-U interface, an S11 interface,and S5-U interface, respectively.

UPF+PGW-U 320 may include a network device (e.g., a converged node) thatprovides UPF functionality for 5G and user plane functionality for 4G.SMF+PGW-C 322 may maintain an anchor point for intra/inter-RAT mobility,maintain an external Packet Data Unit (PDU) point of interconnection toa data network (e.g., DN/PDN 160), perform packet routing andforwarding, perform the user plane part of policy rule enforcement,perform packet inspection, perform lawful intercept, perform trafficusage reporting, enforce QoS policies in the user plane, perform uplinktraffic verification, perform transport level packet marking, performdownlink packet buffering, send and forward an “end marker” to a RANnode (e.g., eNodeB 125), and/or perform other types of user planeprocesses. UPF+PGW-U 320 may communicate with SMF+PGW-C 322 using an N4interface and connect to DN/PDN 160 using an N6 interface (not shown).

PCF+PCRF 324 may support policies to control network behavior, providepolicy rules to control plane functions (e.g., to SMF+PGW-C 322), accesssubscription information relevant to policy decisions, make policydecisions, and/or perform other types of processes associated withpolicy enforcement. PCF+PCRF 324 may specify QoS policies based on QoSflow identity (QFI) consistent with, for example, 5G network standards.

HSS+UDM 326 may store subscription information associated with UEdevices 110 and/or information associated with users of UE devices 110.For example, HSS+UDM 326 may store subscription profiles that includeauthentication, access, and/or authorization information. Eachsubscription profile may include information identifying UE device 110,authentication and/or authorization information for UE device 110,services enabled and/or authorized for UE device 110, device groupmembership information for UE device 110, and/or other types ofinformation associated with UE device 110.

In FIG. 3, when UE device 110 is handed off from eNB 125 to gNB 135, forexample, MME 316 communicates with AMF 306 to provide AMF 306 withinformation about UE device 110 (e.g., bearer information) over an N26interface. The inter-system communication between MME 316 and AMF 306prevents core network 140 from having to change bearers or having to gothrough the process of recycling network resources already allocated forUE device 110.

FIG. 4 is a diagram illustrating exemplary components of a device 400that may correspond to one or more of the devices described herein. Forexample, device 400 may correspond to components included in UE device110, eNB 125, gNB 135, and network devices 145 (such as AMF 306, MME316, SGW 318, and UPF+PGW-U 320). As illustrated in FIG. 4, according toan exemplary embodiment, device 400 includes a bus 405, a processor 410,a memory/storage 415 that stores software 420, a communication interface425, an input 430, and an output 435. According to other embodiments,device 400 may include fewer components, additional components,different components, and/or a different arrangement of components thanthose illustrated in FIG. 4 and described herein.

Bus 405 includes a path that permits communication among the componentsof device 400. For example, bus 405 may include a system bus, an addressbus, a data bus, and/or a control bus. Bus 405 may also include busdrivers, bus arbiters, bus interfaces, and/or clocks.

Processor 410 includes one or multiple processors, microprocessors, dataprocessors, co-processors, application specific integrated circuits(ASICs), controllers, programmable logic devices, chipsets,field-programmable gate arrays (FPGAs), application specificinstruction-set processors (ASIPs), system-on-chips (SoCs), centralprocessing units (CPUs) (e.g., one or multiple cores), microcontrollers,and/or some other type of component that interprets and/or executesinstructions and/or data. Processor 410 may be implemented as hardware(e.g., a microprocessor, etc.), a combination of hardware and software(e.g., a SoC, an ASIC, etc.), may include one or multiple memories(e.g., cache, etc.), etc. Processor 410 may be a dedicated component ora non-dedicated component (e.g., a shared resource).

Processor 410 may control the overall operation or a portion ofoperation(s) performed by device 400. Processor 410 may perform one ormultiple operations based on an operating system and/or variousapplications or computer programs (e.g., software 420). Processor 410may access instructions from memory/storage 415, from other componentsof device 400, and/or from a source external to device 400 (e.g., anetwork, another device, etc.). Processor 410 may perform an operationand/or a process based on various techniques including, for example,multithreading, parallel processing, pipelining, interleaving, etc.

Memory/storage 415 includes one or multiple memories and/or one ormultiple other types of storage mediums. For example, memory/storage 415may include one or multiple types of memories, such as, random accessmemory (RAM), dynamic random access memory (DRAM), cache, read onlymemory (ROM), a programmable read only memory (PROM), a static randomaccess memory (SRAM), a single in-line memory module (SIMM), a dualin-line memory module (DIMM), a flash memory (e.g., a NAND flash, a NORflash, etc.), and/or some other type of memory. Memory/storage 415 mayinclude a hard disk (e.g., a magnetic disk, an optical disk, amagneto-optic disk, a solid state disk, etc.), a Micro-ElectromechanicalSystem (MEMS)-based storage medium, and/or a nanotechnology-basedstorage medium. Memory/storage 415 may include a drive for reading fromand writing to the storage medium.

Memory/storage 415 may be external to and/or removable from device 400,such as, for example, a Universal Serial Bus (USB) memory stick, adongle, a hard disk, mass storage, off-line storage, network attachedstorage (NAS), or some other type of storing medium (e.g., a compactdisk (CD), a digital versatile disk (DVD), a Blu-Ray disk (BD), etc.).Memory/storage 415 may store data, software, and/or instructions relatedto the operation of device 400.

Software 420 includes an application or a program that provides afunction and/or a process. Software 420 may include an operating system.Software 420 is also intended to include firmware, middleware,microcode, hardware description language (HDL), and/or other forms ofinstruction. Additionally, for example, UE device 110 may include logicto perform tasks, as described herein, based on software 420.

Communication interface 425 permits device 400 to communicate with otherdevices, networks, systems, devices, and/or the like. Communicationinterface 425 includes one or multiple wireless interfaces and/or wiredinterfaces. For example, communication interface 425 may include one ormultiple transmitters and receivers, or transceivers. Communicationinterface 425 may include one or more antennas. For example,communication interface 425 may include an array of antennas.Communication interface 425 may operate according to a protocol stackand a communication standard. Communication interface 425 may includevarious processing logic or circuitry (e.g.,multiplexing/de-multiplexing, filtering, amplifying, converting, errorcorrection, etc.).

Input 430 permits an input into device 400. For example, input 430 mayinclude a keyboard, a mouse, a display, a button, a switch, an inputport, speech recognition logic, a biometric mechanism, a microphone, avisual and/or audio capturing device (e.g., a camera, etc.), and/or someother type of visual, auditory, tactile, etc., input component. Output435 permits an output from device 400. For example, output 435 mayinclude a speaker, a display, a light, an output port, and/or some othertype of visual, auditory, tactile, etc., output component. According tosome embodiments, input 430 and/or output 435 may be a device that isattachable to and removable from device 400.

Device 400 may perform a process and/or a function, as described herein,in response to processor 410 executing software 420 stored bymemory/storage 415. By way of example, instructions may be read intomemory/storage 415 from another memory/storage 415 (not shown) or readfrom another device (not shown) via communication interface 425. Theinstructions stored by memory/storage 415 cause processor 410 to performa process described herein. Alternatively, for example, according toother implementations, device 400 performs a process described hereinbased on the execution of hardware (processor 410, etc.).

FIGS. 5-8 are signal flow diagrams illustrating exemplary communicationsin a portion 500 of network environment 100 for triggering a return to a5G connection after concluding a call with VoLTE fallback. As shown inFIGS. 5-8, network portion 500 may include UE device 110, eNB 125, MME316, AMF 306, gNB 135, and IMS network 150. Each of FIGS. 5-8 relates todifferent embodiments where eNB 215 triggers a handover procedure fromeNB 125 (e.g., RAN 120) to gNB 135 (e.g., RAN 130) at the completion ofa VoLTE call from a 5G-capable UE device 110. Assume, in each of FIGS.5-8, that UE device 110 is 5G-capable (e.g., NR standalone-capable) in acoverage area that does not support VoNR, such as described above inconnection with FIG. 2. Further assume that when a voice call starts, UEdevice 110 is redirected or performs an inter-RAT handover from gNB 135(e.g., RAN 130) to eNB 125 (e.g., RAN 120) when the dedicated bearerrequired for the voice call is set up.

Referring to FIG. 5, communications to trigger a fast return to 5Gservice may be included in an RRC Connection Reconfiguration message. Asshown at reference 505, UE device 110 may simultaneously conduct a VoLTEcall and separate data activity (e.g., a game, a video stream, livescores, etc.). eNB 125 may detect the end of the VoLTE call, asindicated at reference 510. As soon as the VoLTE call is over, eNB 125may send a RRC Connection Reconfiguration message to release the VoLTEbearer (e.g., a QCI-1 bearer) including some parameter reconfiguration(e.g., a connected mode discontinuous reception (cDRX) setting) inaccordance with conventional protocols. According to an implementation,however, and as shown at reference 515, eNB 125 may use the same RRCConnection Reconfiguration message to trigger a handover to 5G byconfiguring a B1 measurement (e.g., for LTE event B1, per 3GPP TS36.331) on designated neighboring NR bands (e.g., to detect if aneighbor cell is better than an absolute threshold). This modified RRCConnection Reconfiguration message will trigger a measurement report ofthe NR bands from UE device 110 if the UE is still in a NR coverage area(e.g., coverage area 220). Thus, UE device 110 may perform signalmeasurements 520 and provide a NR measurement report 525 to eNB 125.Once the NR measurement reports is received, eNB 125 may initiate aninter-RAT handover 530 back to 5G service (e.g., via gNB 135)immediately. For example, eNB 125 may signal MME 316, which may utilizean N26 interface with AMF 306 to transfer information for UE 110.

According to FIG. 6, communications to trigger a fast return to 5Gservice are initiated through a blind redirection at the end of a VoLTEcall. Similar to FIG. 5, UE device 110 may simultaneously conduct aVoLTE call and separate data activity, as shown in reference 605, andeNB 125 may detect the end of the VoLTE call, as indicated at reference610. As soon as the VoLTE call is over, eNB 125 may perform a blindredirection for UE device 110. More particularly, eNB 125 may send a RRCrelease message w/redirection to another RAT (e.g., gNB 135 for RAN 130)based on an Inter-RAT neighbor list configuration stored by eNB 125. Forexample, eNB 125 may transmit a RRC Connection Release message 620 to UEdevice 110. Thereafter, UE device 110 may re-establish a RRC connectionvia the 5G NR RAN (e.g., gNB 135), as indicated by reference 625.

In contrast with the modified RRC Connection Reconfiguration messagedescribed in connection with FIG. 5, the blind redirection process ofFIG. 6 may be faster, since UE device 110 does not need to measure NRbands and can immediately search for NR bands for a reattachment.Furthermore, the blind redirection of FIG. 6 may be used in RANs that donot support the N26 interface. If UE device 110 moves out of a NRcoverage area during the VoLTE call, UE device 110 will fail to find NRbands and come back to search LTE bands and continue data service usingRAN 120/eNB 125.

Referring to FIG. 7, eNB 125 may configure B1 event measurements at thestart of a VoLTE call to reduce measurement latency that may occurthrough the modified RRC Connection Reconfiguration message described inconnection with FIG. 5. Similar to FIG. 5, UE device 110 maysimultaneously conduct a VoLTE call and separate data activity, as shownin reference 705. Based on the VoLTE call connection (e.g., as soon asthe VoLTE call is started), eNB 125 may configure NR B1 measurement onNR bands, as indicated by reference 710. For example, eNB 125 may send aRRC Connection Reconfiguration message with the measurementconfiguration. The NR B1 measurement configuration may cause UE 110 toperform NR signal measurements, as shown in reference 715, and trigger ameasurement report 720 from UE device 110 if certain conditions are met.

In the measurement configuration 710, eNB 125 can configure reportingconfigurations in the RRC Connection Reconfiguration message to “reporton leave,” so that UE device 110 will send the measurement report 720 ifthe radio frequency (RF) condition for entering the condition no longerexists. In this way, eNB 125 is “stateful” when it comes to the UEdevice 110 measurement report 720. When VolTE call ends 725, eNB 125 canuse the measurement report (or lack thereof) to determine whether totrigger a 4G-to-5G inter-RAT handover 730. For example, if measurementreport 720 indicates that UE device 110 is still in NR coverage, of ifno measurement report 720 is received (e.g., indicating UE device 110did not leave NR coverage), eNB 125 may initiate a 4G-to-5G inter-RAThandover.

Given the NR B1 measurement configuration at the start of a VoLTE call,it is probable that UE device 110 will report NR band measurement duringthe VoLTE call. Upon the end of VoLTE call, if no additional measurementreport is received from the UE device 110 regarding NR bandsmeasurement, eNB 125 may conclude that condition has not changed. eNB125 may, therefore, use the “last” measurement report to perform a 4G to5G handover. Otherwise, UE device 110 will not report B1 measurement aslong as the RF criteria are met. Once a measurement report is received,eNB 125 can evaluate if the NR bands still meet the condition for ahandover to 5G. Because the measurement configuration to “report onleave” would result in UE device 110 sending a report only when the RFcondition for the NR bands is not acceptable (e.g., out of the coveragearea 220 of gNB 135), eNB 125 would determine the NR bands do not meetthe condition for a handover.

Referring to FIG. 8, communications to trigger a fast return to 5Gservice may also be applied during a EN-DC connection, such an EN-DCconnection where eNB 125 serves as an anchor for a 5G NR connection viagNB 135. In the example of FIG. 8, UE device 110 may simultaneouslyconduct a VoLTE call and separate data activity over an EN-DC connectionthat uses both LTE and NR connections for a data session, as shown inreference 805. eNB 125 may detect the end of the VoLTE call, asindicated at reference 810. If UE device 110 is configured with an EN-DCconnection while a VoLTE call is released, eNB 125 may send an RRCConnection Reconfiguration message 815 to release the VoLTE bearer(e.g., a QCI-1 bearer) and at the same time may trigger an immediateInter-RAT handover to the NR leg of the previous EN-DC connection (e.g.,without any B1 measurement). As indicated by reference 820, eNB 125 andgNB 135 may participate in an Inter-RAT handover to switch UE device 110over to 5G NR standalone operation with gNB 135.

The post VoLTE communications in FIG. 8 can maintain service continuity,since eNB 125, as the LTE anchor for the EN-DC connection, is stillaccessible from coverage area 210 (FIG. 2) even if UE device 110 is notin NR coverage (e.g., within coverage area 220). Once the NR leg for theEN-DC connection is successfully added in a non-standalone mode (e.g.,UE device 110 is indeed in a NR coverage area), then eNB 125 can takethe action of inter-RAT handover to standalone mode, as indicated byreference 830. The communications of FIG. 8 are exemplary. In otherimplementations, eNB 125 can send the first RRC ConnectionReconfiguration message 815 to release the QCI-1 bearer, andsubsequently send a second RRC Connection Reconfiguration message (notshown) to trigger the handover to 5G service. Above solution can be usedon a NR carrier that supports both non-standalone and standaloneoperations.

FIG. 9 is a flow diagram illustrating an exemplary process 900 to bringa 5G standalone-capable end device back into 5G service as soon as aVoLTE call is over, according to an implementation described herein. Inone implementation, process 900 may be implemented by eNB 125. Inanother implementation, process 900 may be implemented by an eNB 125 inconjunction with one or more other devices in network environment 100.

Referring to FIG. 9, process 900 may include receiving a fallbackconnection to a 4G network for a voice call (block 910) and determiningif the end device is 5G NR standalone capable (block 920). For example,eNB 125 (or another wireless station) may receive a handover for afallback connection from gNB 135 (e.g., RAN 130) to support a VoLTE callon UE device 110. eNB 125 may receive information from UE device 110 andor other network devices indicating that UE device 110 is 5G NRstandalone-capable.

If the end device is 5G NR standalone capable (block 920—Yes), process900 may further include detecting an end of the voice call (block 930)and initiating an immediate handover from the 4G network to the 5Gnetwork (block 940). For example, eNB 125 may detect an end of the VoLTEcall, and initiate, in response to the detecting, a handover of the UEdevice 110 back to the RAN 130/gNB 135. According to implementationsdescribed herein, eNB 125 may initiate the handover while UE device 110is still in a radio resource control (RRC) connected mode.

If the end device is not 5G NR standalone capable (block 920—No),process 900 may hold the existing session open until an RCC idle modeoccurs (block 950). For example, if UE device 110 is not 5G NRstandalone-capable, eNB 110 may follow conventional procedures to waitfor UE device 110 to perform higher priority system selection when UEdevice 110 transitions to an RRC idle mode.

The foregoing description of implementations provides illustration anddescription, but is not intended to be exhaustive or to limit theinvention to the precise form disclosed. Modifications and variationsare possible in light of the above teachings or may be acquired frompractice of the invention. For example, while a series of blocks havebeen described with regard to FIG. 7, the order of the blocks andmessage/operation flows may be modified in other embodiments. Further,non-dependent blocks may be performed in parallel.

Certain features described above may be implemented as “logic” or a“unit” that performs one or more functions. This logic or unit mayinclude hardware, such as one or more processors, microprocessors,application specific integrated circuits, or field programmable gatearrays, software, or a combination of hardware and software.

To the extent the aforementioned embodiments collect, store or employpersonal information of individuals, it should be understood that suchinformation shall be collected, stored and used in accordance with allapplicable laws concerning protection of personal information.Additionally, the collection, storage and use of such information may besubject to consent of the individual to such activity, for example,through well known “opt-in” or “opt-out” processes as may be appropriatefor the situation and type of information. Storage and use of personalinformation may be in an appropriately secure manner reflective of thetype of information, for example, through various encryption andanonymization techniques for particularly sensitive information.

Use of ordinal terms such as “first,” “second,” “third,” etc., in theclaims to modify a claim element does not by itself connote anypriority, precedence, or order of one claim element over another, thetemporal order in which acts of a method are performed, the temporalorder in which instructions executed by a device are performed, etc.,but are used merely as labels to distinguish one claim element having acertain name from another element having a same name (but for use of theordinal term) to distinguish the claim elements.

No element, act, or instruction used in the description of the presentapplication should be construed as critical or essential to theinvention unless explicitly described as such. Also, as used herein, thearticle “a” is intended to include one or more items. Further, thephrase “based on” is intended to mean “based, at least in part, on”unless explicitly stated otherwise.

In the preceding specification, various preferred embodiments have beendescribed with reference to the accompanying drawings. It will, however,be evident that various modifications and changes may be made thereto,and additional embodiments may be implemented, without departing fromthe broader scope of the invention as set forth in the claims thatfollow. The specification and drawings are accordingly to be regarded inan illustrative rather than restrictive sense.

All structural and functional equivalents to the elements of the variousaspects set forth in this disclosure that are known or later come to beknown to those of ordinary skill in the art are expressly incorporatedherein by reference and are intended to be encompassed by the claims. Noclaim element of a claim is to be interpreted under 35 U.S.C. § 112(f)unless the claim element expressly includes the phrase “means for” or“step for.”

1. A method, comprising: receiving, by a wireless station, a fallbackconnection, for a Fifth Generation (5G) New Radio (NR)standalone-capable end device, from a second network to a first networkto support a voice call on the end device, wherein the fallbackconnection supports a voice-over-Long Term Evolution (VoLTE) call;detecting, by the wireless station, an end of the VoLTE call; andinitiating, by the wireless station and based on the detecting, ahandover of the end device back to the second network, wherein theinitiating occurs while the end device is in a radio resource control(RRC) connected mode, and wherein the initiating includes sending, tothe end device, a RRC Release message with redirection instructions tothe second network.
 2. The method of claim 1, wherein wireless stationincludes an evolved Node B for an Evolved Universal MobileTelecommunications System (UMTS) Terrestrial Radio Access Network(E-UTRAN), wherein the first network includes the E-UTRAN for an LTEnetwork, and wherein the second network device includes a 5G network. 3.The method of claim 1, wherein the initiating includes sending to theend device, within an RRC Connection Reconfiguration message, radiomeasurement configurations for NR frequency bands.
 4. The method ofclaim 1, further comprising: sending, in response to the receiving, a B1measurement configuration to the end device during the VoLTE call. 5.The method of claim 4, wherein the B1 measurement configurationinstructs the end device to provide a measurement report when the enddevice detects leaving a coverage area of the second network.
 6. Themethod of claim 5, wherein the initiating further comprises: directing,based on a failure to receive the measurement report, the handover ofthe end device back to the second network.
 7. (canceled)
 8. The methodof claim 1, wherein sending the RRC Release message includes sending theRRC Release message without relying on a signal measurement from the enddevice.
 9. The method of claim 1, further comprising: identifying, bythe eNB, an Evolved Universal Mobile Telecommunications System (UMTS)Terrestrial Radio Access Network (E-UTRAN)-NR Dual Connectivity (EN-DC)capability of the end device, wherein the initiating further comprisesprompting an inter-radio access technology (RAT) handover to astandalone connection with the second network.
 10. A network devicecomprising: an interface to wirelessly communicate with end devices viaa first wireless network; a memory device to store a set ofprocessor-executable instructions; and a processor configured to executethe processor-executable instructions, wherein executing theprocessor-executable instructions causes the processor to: receive afallback connection, for a Fifth Generation (5G) New Radio (NR)standalone-capable end device, from a second network to the firstnetwork to support a voice call on the end device, wherein the fallbackconnection supports a voice-over-Long Term Evolution (VoLTE) call,detect an end of the VoLTE call, and initiate, based on the detecting, ahandover of the end device back to the second network, wherein theinitiating occurs while the end device is in a radio resource control(RRC) connected mode, and wherein the initiating includes sending, tothe end device, a RRC Release message with redirection instructions tothe second network.
 11. The network device of claim 10, wherein thenetwork device includes an evolved Node B for an Evolved UniversalMobile Telecommunications System (UMTS) Terrestrial Radio Access Network(E-UTRAN).
 12. The network device of claim 10, wherein, when theprocessor detects an end of the VoLTE call, the processor is furtherconfigured to: detect a data session on the first network that continuesafter the end of the VoLTE call.
 13. The network device of claim 10,wherein the first network includes a LTE network, and wherein the secondnetwork device includes a 5G network.
 14. The network device of claim10, wherein, when the processor initiates the handover, the processor isfurther configured to: send, to the end device and within an RRCConnection Reconfiguration message, radio measurement configurations forNR frequency bands.
 15. The network device of claim 10, wherein theprocessor is further configured to: send, in response to receiving thefallback connection, a B1 measurement configuration to the end deviceduring the VoLTE call, wherein the B1 measurement configurationinstructs the end device to provide a measurement report when the enddevice detects leaving a coverage area of the second network.
 16. Thenetwork device of claim 10, wherein, when the processor initiates thehandover, the processor is further configured to: send, to the enddevice, a release message for the first network with redirectioninstructions to the second network.
 17. The network device of claim 10,wherein the processor is further configured to: identify an EvolvedUniversal Mobile Telecommunications System (UMTS) Terrestrial RadioAccess Network (E-UTRAN)-NR Dual Connectivity (EN-DC) capability of theend device.
 18. A non-transitory computer-readable medium containinginstructions executable by at least one processor, the non-transitorycomputer-readable medium comprising one or more instructions to causethe at least one processor to: receive, by a wireless station, afallback connection, for a Fifth Generation (5G) New Radio (NR)standalone-capable end device, from a second network to the firstnetwork to support a voice call on the end device, wherein the fallbackconnection supports a voice-over-Long Term Evolution (VoLTE) call;detect, by the wireless station, an end of the VoLTE call; and initiate,by the wireless station and based on the detecting, a handover of theend device back to the second network, wherein the initiating occurswhile the end device is in a radio resource control (RRC) connectedmode, and wherein the initiating includes sending, to the end device, aRRC Release message with redirection instructions to the second network.19. The non-transitory computer-readable medium of claim 18, wherein theinstructions to initiate the handover further include instructions to:identify whether the end device has an E-UTRAN-NR Dual Connectivity(EN-DC) capability; send, after the detecting and based on theidentifying, instructions to initiate a non-standalone connection withthe 5G NR network via the wireless station when the end device has theEN-DC capability; and send, to the end device and within an RRCConnection Reconfiguration message, radio measurement configurations forNR frequency bands when the end device does not have the EN-DCcapability.
 20. The non-transitory computer-readable medium of claim 19,further comprising instructions to cause the at least one processor to:send, to the end device, a RRC Release message with redirectioninstructions to the second network and without relying on a signalmeasurement from the end device.
 21. The network device of claim 10,wherein the processor is further configured to: store, in the memorydevice, an inter-radio access technology (RAT) neighbor list, andwherein the initiating further comprises providing direction to anotherwireless station based on the inter-RAT neighbor list.